1. Field of the Invention
This invention relates to a unique construction method for a multi-touch resistive touch-screen sensor.
2. Statement of the Problem
Different technologies exploit various parameters of layered materials to make sensors. Current resistive sensors are constructed to hold two linearly resistive layers apart at rest that are allowed to come into contact upon a touch event. The resistor dividers resulting from a touch are read by control electronics and a location is calculated. Capacitive sensors are constructed from conductive layers that are driven by signals to generate an electric field. When the base capacitance is altered by another electric field, a user's finger for example, the differences are measured by control electronics and a location is calculated. Inductive sensors are driven by signals to generate a magnetic field. When the magnetic field is altered by another magnetic field, a stylus with a coil for example, the differences are measured by control electronics and a location is calculated. Surface Acoustic Wave sensors use transducers to initiate mechanical waves in a sensor, and control electronics process the reflected wave pattern to look for changes caused by touch points reflecting and/or absorbing the wave energy to calculate a location. IR sensors shine a grid of beams across the sensor surface that is monitored on opposing sides. A touch breaks the beam and the control electronics determine a location.
Of these sensor technologies, resistive has distinct advantages. Resistive sensors are like mechanical switches so respond to touches from all actuators such as fingers, even when gloved, and common implements like pencils or pens. A touch is not ambiguous because the same pressure that informs the electronics of a touch informs the user of a touch. Resistive also has a high signal to noise ratio allowing for the possibility of high resolution.
The primary disadvantages of current resistive touchscreens are optical clarity and durability. Both of these disadvantages are due to a sensor construction that requires a thin air gap between two clear conductive coating layers. This construction reduces optical clarity by adding additional reflective layers due to the miss match of the index of refraction between air and the clear conductive coatings. Durability is compromised by repeated contact of the two delicate clear conductive coatings and a top sheet that is soft to allow for mechanical deflection.